In recent years, a small-size and low-profile imaging unit has been mounted on a portable terminal of an electronic device, such as a cellular phone or a PDA (Personal Digital Assistant). Such an imaging unit is generally provided with a solid-state image sensor such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide Semiconductor) image sensor, and a lens group for forming an image in a light receiving area of the solid-state image sensor.
With reduction in size and profile of portable terminals and wide use of the portable terminals, there has been a demand for further reduction in the size and profile of imaging units mounted on the portable terminals while the productivity thereof is also requested. In response to such a request, there has been proposed a technique for mass-producing modules of a lens array laminate in such a manner that a large number of lenses and coupling portions for coupling those lenses with one another are integrally formed out of a photocuring or thermosetting resin material to thereby constitute each lens array, the lens arrays are put into a plurality of layers to form a lens array laminate, and the lens array laminate is divided into a plurality of modules each including a group of lenses arrayed in the laminating direction (see Patent Literature 1 (WO 08/153,102)).
In an imaging unit mounted on a cellular phone or the like, accuracy of alignment of μm order is typically required in a group of lenses. The accuracy of alignment in the group of lenses depends on the pitch accuracy of the lenses in each lens array. In the technique disclosed in Patent Literature 1, for example, an error in pitch among lenses may appear due to influence of variation in light intensity or temperature during curing of a resin material. In addition, an error in pitch among lens forming surfaces of molds for molding the resin material or deformation of a lens array caused by the release of the lens array from the mold may cause the error in pitch among the lenses. Due to a series of such error factors, it has been difficult to suppress the error in pitch among the lenses down to the order of μm in the whole lens array according to the technique disclosed in Patent Literature 1.
To solve the foregoing problem, in a lens array in which a large number of lenses and a coupling portion coupling the lenses with one another are formed integrally, there has been proposed a technique for forming slits in the coupling portion to give flexibility to the coupling portion so that the error in pitch among the lenses can be absorbed by deformation of the coupling portion (see Patent Literature 2 (JP-A-2004-226872)).